Heretofore, on most conventional tractors and mobile construction machines such as backhoes, the operator when working the hydraulic tools associated with the equipment, normally place the throttle for the engine close to maximum. This ensures sufficient power for operating the hydraulic pump for supplying pressurized hydraulic fluid to the cylinders used for manipulating the tools. One problem with such a method of operation is that when the tool was not being used, either momentarily or for longer periods of time, the engine would often be allowed to continue running at maximum throttle consuming a substantial amount of fuel as well as producing unnecessary wear thereon.
There are several devices shown in patents for regulating the fuel to internal combustion engines used in tractor vehicles responsive directly to load requirements for automatically permitting additional fuel to be delivered to the engine. Examples of such devices are disclosed in U.S. Pat. Nos. 2,986,291, 3,542,228, 3,901,395, 3,792,791, 3,606,049 and 3,148,790. The majority of these systems appear to be quite complicated compared to the simple construction of applicant's device.